Cooling fans inside Hub motors

[Cowardlyduck]

Since the motor is moving why not bore holes and put fan blades on the rotor as John did ? Most electric motors have built in fan blades way more simple solution.

Because that requires high motor speeds to function and stops working when the bike stops moving. I suggest you read the rest of this thread to get an understanding of the kind of requirements that have driven this modification.

I have to mount the air duct and cover the large holes with plastic. Is epoxy the best way to do this?<br abp="682"><br abp="683">The only other alternative I can think is to tap small holes and use tiny screws to hold everything together.

I would use epoxy. If it fails you can always try again with screws where as if you try screws first you will be left with holes.

Cheers

 

[madin88]

not sure if epoxy is a good solution (depends on material and surface of airduct).
i would use some sort of Sika adhesive. i have made good experience with Sikaflex 552.

 

[Offroader]

With all this trouble and mess using epoxy and other adhesives, I think I'm going to just tap small holes for tiny screws. This way everything is guaranteed to hold firm, and if I need to change out anything I simply just unscrew it.

I never tapped really tiny screw holes but I don't see the big deal?

I could also possibly cover the holes in the center of my cromotor with heat sinks instead of just plastic if I tap some holes to screw them down. Not sure how much of a difference this makes as it will only have contact on the endges but it must help pull heat away from the stator.

Would also be nice if I could find convex heat sinks to go around the inside of the stator, I heard you could heat regular aluminum heat sinks and try and shape them to the surface.

You can see what I have to work with here, I could put heat sinks on the inside of the stator this would really help pull heat away and has lots of surface area if I could figure out how to get a convex heat sink. I could also fill in the holes with a heat sink, but it would only pull heat from the edges, but should be enough.

 

[madin88]

small holes is no bad idea. it should be possible to cut M2,5 thread on top of the stator holder.
about heatsinks, you could use many small ones side by side. for instance:
http://www.ebay.com/itm/1PC-Heat-Si...938?pt=LH_DefaultDomain_0&hash=item56747bec52
or somethinge like this and bend it:
http://www.alutronic.de/produkte/kuehlkoerper-profile/standard-kammprofile/123/pr167?c=1331
as glue i would use some kind of 1h epoxy for metal or other special glue with good thermal conductivity

btw: do you place the bldc controller for the fan inside the motor, or do you leave it outside?

 

[Offroader]

madin, I'm thinking of using m1.4 or m1.6 screws. m2.5 is very large screws for holding almost no weight. Any reason you would find a m1.4 or m1.6 too small?

I just picked up a m1.6 screw and it is pretty large, so I may actually buy m1.4 screws. I may use a combination of both. I will have to buy stainless bolts, but I don't think it will have any issues with the aluminum stator?

I plan on putting the ESC outside because I may run the fan at lower RPM and am not sure if that will heat up the ESC. The other issue is I heard these ESC also tend to blow and if running the fan at lower RPM causes issues I can easily replace the ESC rather than having to open the motor.

 

[madin88]

M2,5 was only for example. i see no reason why smaller thread should not also be OK for this purpose.
its a good idea to place the fan controller outside the motor. the reason why cheapo rc bldc controller often blow is they do not like throttle between 50 and 99%. if you stay out of this range it should hold or just use the next larger controller.
YGE from germany makes very good rc controller and they have a function called "active freewheel" so you can use the whole throttle band wihtout beeing afraid of blowing it or overheating. though these esc are quite expensive..

 

[Offroader]

I'm making some progress and should have this running by the end of the week.

The EDF fan blows a lot of air and the gap between the stator and magnets is very small. I wonder if this will restrict the air flow. Maybe the gap when taking into account the whole gap area is bigger than I think and will allow more air flow than I think.

This should work very well, almost like a hair dryer if it works how it is intended. The airflow will hit all the copper windings at both sides of the stator with good force. This should have the potential to solve all the heat related problems I could ever have and is rather simple to implement. The only issue I see is the small gap between the stator and windings being too small to allow a strong airflow.

I've also ordered a cheap temp control switch NTC10k to play around with. The hysteresis only allows me up to 15c range. So I could set to turn the fans on at 90c and off at 75c. I'm not sure if that range is large enough to not be annoying with the the fans constantly turning on and off.

Is there an efficient temp heat range to run a cromotor at?

 

[Routybouty]

Is this a brushless EDF with ESC? I don't think a temp switch will help if so. Most ESCs require a minimum throttle input to initialize (if you're looking for something fully automatic). I suppose a little pic board with a temp sensor could control the PWM to the ESC, wouldn't be too hard for some fancy control. Looking forward to the results !

 

[Cowardlyduck]

I'm really enjoying follow your progress Offroader...please keep posting as you go.

I'm still making very slow progress on my mod. I ended up soldering in my series connections for the fans on my controller as the JST connectors I had previously connected were just cheap one's with thin wire and I was worried they would over-heat.
My rough calculations estimate with my 9 fans running in series, I will be pulling about 50W including losses, when running all 9 fans off a 52V nominal battery in series.
I don't really know how series connections work exactly for current flow, but I 'think' that means some of the wires will be carrying 5+ amps! That makes me glad I used 24 and 20AWG Silicone wire for the connections and long runs, but it does make me wonder if the thin wires that come on the fans as stock will be able to handle that much current for long periods.
Does anyone know if the every connection carries the full amp load in series connections, or does it reduce between each load?

So far I count 3 way's the fans in this mod can be powered:
1) Using a DC-DC converter. As per my first attempt.

2) Using EDF fans with an ESC as Offroader is doing.

3) Directly running the fans in series. As per my current attempt.

Each method has it's advantages and disadvantages. I think the EDF solution is the best for cooling, but potentially more complex, and expensive than other methods. It's also probably louder...if you care about such things, but my Yeah Racing fans are pretty loud also. I think the key here is being able to turn them on/off as required.

Cheers

 

[madin88]

Does anyone know if the every connection carries the full amp load in series connections, or does it reduce between each load?

if you have nominal voltage across one fan and all fans are identical than you also have nominal current. it will not multiply in series connection (in parallel it would).

The only issue I see is the small gap between the stator and windings being too small to allow a strong airflow.

thats why i would leave a gap between airduct and aluminum stator for more airflow because it certainly will improve cooling.

Is there an efficient temp heat range to run a cromotor at?

check copper resistance at differenet temperatures. you'll see the cooler the motor, the more efficient it is
the higher the phase current, the more it becomes an issue (losses are I² x R).

 

[Cowardlyduck]

if you have nominal voltage across one fan and all fans are identical than you also have nominal current. it will not multiply in series connection (in parallel it would).

So if I understand you correctly, each link between each fan will only see the amp load of one fan equivalent. That's only about 1 amp, so that sounds a lot better for the wires survival.

Cheers

 

[Offroader]

I actually meant the gap between the stator and magnets, not very much room there for the air flow to circulate, but maybe there is.

 

[Cowardlyduck]

I'm not sure how/why I thought my air flow was going to be right>left, disc side>Freewheel side, but doing some tests (off the bike) last night, I discovered it's the opposite!
Looking back at my pictures, it makes sense to me now...I'm not sure why I ever thought it would be the other way around.
I realised however that air flow exiting the disc side is actually better anyway. The disc creates some centrifugal air flow on it's own. Together with the fan air flow pushing air out on that side, they aide each other for increased flow.
I could even add an impeller under the disc to help push even more air, however I'm not sure if that would create problems as the air rushed past the holes with air pushing out from them.

Cheers

 

[Routybouty]

Talking about this one?

http://endless-sphere.com/forums/viewtopic.php?f=31&t=68373

 

[Cowardlyduck]

Talking about this one?

http://endless-sphere.com/forums/viewtopic.php?f=31&t=68373

Yeah I did see that...problem is for me at least, the air flow is the wrong way around.

I think if someone designed a cooling fan mod with one of those impellers in mind the combination of both could move a huge amount of air. Doing it that way could even make it realistically viable to use dust filters without loosing so much air flow that it wasn't effective.

Cheers

 

[amberwolf]

I could even add an impeller under the disc to help push even more air, however I'm not sure if that would create problems as the air rushed past the holes with air pushing out from them.

It is possible, even likely, that the air passing the holes will cause a venturi effect and pull air *faster* out the holes.

 

[Cowardlyduck]

It is possible, even likely, that the air passing the holes will cause a venturi effect and pull air *faster* out the holes.

Thanks for the input AW.
I think you might be right...but right now, I just need to get this thing up and running. I'll worry about impellers to increase air-flow if I find the existing setup is not enough (which I doubt)
That being said, it would be a good idea for those who don't want to bother with fans and just vent there hubs.

Cheers

 

[Offroader]

As a temporary test I taped up all the holes in my stator and mounted the EDF with one side cover off.

THE EDF blows a lot of air when holding it outside the motor, but when installed in the motor it doesn't seem to come around the stator with much force. You do feel a slight breeze coming through but not nearly as strong as holding it in the air and pointing it at your face.

I think the problem is the air is being dispersed or spread out in such a large area that it doesn't have much force, reason is because it does seem to be sucking in a good amount of air.

SInce it will be almost impossible to get a tight air seal with the air duct, I don't know how much fresh air is going to be sucked in vs how much is just going to be recirculated. I don't know how much fresh air is needed for cooling.

I'll have to test it out with the single fan and possibly add more EDF fans. I'm not sure if a single EDF fan will be enough to get the air flow that I need.

The other issue is there is a gap between the windings and side cover, a good size gap like 15mm, so a lot of air is going to completely miss blowing through the windings. I could consider adding another air duct on the side covers to close up this gap forcing at least double the air flow to go through the windings at the side. I'm not sure if this is necessary as I don't know how important it is to have the air flowing through those copper windings on the sides of the stator.

 

[Cowardlyduck]

Offroader, don't discount how much effect even a small amount of air flow through the hub will have...remember my previous tests...
http://endless-sphere.com/forums/viewtopic.php?f=30&t=56965&start=25#p946731

I'm sure even a single EDF will move more than 6 12V Laptop fans running at 18V. Those 6 fans never exceeded 15W total and each was only about 2.1CFM.

Unless your smashing up steep hills non-stop for minutes (probably more than 5) at a time, I wouldn't worry about it, you will still see a great improvement.

Cheers

 

[Offroader]

Is this a brushless EDF with ESC? I don't think a temp switch will help if so. Most ESCs require a minimum throttle input to initialize (if you're looking for something fully automatic). I suppose a little pic board with a temp sensor could control the PWM to the ESC, wouldn't be too hard for some fancy control. Looking forward to the results !

That is what I intend to do is hook up a on/off temp sensor to the signal wire on the ESC, which I belive is the PWM?

I will keep the servo tester on full setting, and the temp control switch will shut this signal on and off. Do you see any issues with this?

 

[Cowardlyduck]

I will keep the servo tester on full setting, and the temp control switch will shut this signal on and off. Do you see any issues with this?

No issues, but I would also add a manual switch so you can turn it on or off if you want to.
There are several reasons I can see an override being useful.
1) They are bloody loud...so even if the motor is a bit warm, in a crowded place, or tunnel etc, you might want to turn the fans off anyway.
2) If your battery is really low...even the small <100W pull of the fans might make a difference to range if the motor will soon cool naturally anyway.
3) Depending on air temp and motor load, in some cases...it might make the motor more efficient for long range to run the fans continuously even if it's not overly hot.
4) Water crossings, or rain...you'll probably want to turn the fans off...even if the motor is hot...although I didn't and was fine previously, but I wouldn't want to push my luck again.

Cheers

 

[Offroader]

cowardlyduck, do you have any idea on what I could use to get 2s lipo voltage, around 8 volts from my 18s battery?

I have a 12 volt 10 amp dc-dc converter but I can't adjust it lower, I opened it up and saw no adjusting pot or anything like that.

I don't want to run my EDF fans at 3s because of failures at those high RPM speeds.

I ordered a couple of more powerful edf 30mm fans that have double the thrust of my 27mm edf. My 27mm edf only pulls 2.2 amps at full throttle at 2s.

I have made some good progress and got a good final plan of making the air duct. I'm happy I waited a bit because I got a lot of good ideas to make everything better. I'm also going to put holes in the bottom of the duct to help pull some air through the windings instead of leaving a gap at the top. I'm going to put something at the top of the duct like some kind of foam that the side cover will wear away flush to prevent any air from flowing through the top of the air duct. If air is going to circulate around better it go at the bottom to pull air through the windings.

I also put some tiny holes where I covered the holes in the center of the stator. This way a little air flows everywhere over the aluminum stator, still with most of the air venting outside.

This thing should really be effective, can't wait to see how good it works. My goal is to only use the fans to quick cooling off rather than keep them on constantly. I like silent operation, but I also don't like the fact that once I use about 800WH of battery power my motor is so heated that I need about an hour for it to cool down or it will just reheat itself in minutes. But of course I will always have the option to turn them on when running the motor hard and needing to keep running hard.

 

[Routybouty]

That is what I intend to do is hook up a on/off temp sensor to the signal wire on the ESC, which I belive is the PWM?

I will keep the servo tester on full setting, and the temp control switch will shut this signal on and off. Do you see any issues with this?

Oic, I thought you were gonna put it on the power to the ESC. When the temp is low the switch will be open, meaning no signal to the ESC. I'm not sure how they react to that, never encountered that situation. I would suggest trying it before you go mounting everything up. I would worry when you first power up the system and the temp switch should be open, there will be no signal to the ESC. They typically want a "throttle low" signal for safety and then they will initialize.

Laptop power supplies or universal supplies, AC in, are pretty easy to make work. I have a few of these that I modified to run at 7V and 12V, they are rated for a minimum of 15V. It just a resistor change on switch, pretty easy, takes 5 minutes. They can run off DC, it doesn't matter. it's the first thing they do on the board anyway is run through a rectifier.

http://www.ebay.com/itm/90W-10tip-U...743?pt=LH_DefaultDomain_0&hash=item1e6ee3d0b7

They are dirt cheap, give 90W out, and have decent packaging.

 

[Cowardlyduck]

Glad to hear your making progress Offroader. I am too...soldered up part of my power tap harness for my fans > main Battery connection yesterday.

cowardlyduck, do you have any idea on what I could use to get 2s lipo voltage, around 8 volts from my 18s battery?

That's a tough one and one of the reasons I no longer run 18S myself. There are pretty much no off the shelf, small DC-DC converters that will take over 60V input and give a decent power output...I've searched everywhere and gave up.

What Routybouty suggested above is pretty much the only way. You need to try an AC adaptor. Many of them will accept a lower voltage DC input and give you the stated output, but not all will work...you need to try them first. The sucky part is...unless you have a collection of appropriate AC adaptors to try, you just have to order one that meets your needs on paper, then try it...it may or may not work. :|

Let us know what you end up doing.

Cheers

 

[Offroader]

Just an update, I've put a lot of time into getting this thing to work. It is taking a lot of time and planning to get it right. I did some testing with airflow and I had to drill more holes in the intake area.

The air does flow well, it doesn't shoot out the holes with crazy force, as either the air is well dispersed and possibly there is lots of leakage that causes air re-circulation.


I have a couple more EDF's, 30mm which put out double the thrust. I'll have to slightly enlarge the stator to fit the 30mm as I need 1 or2mm clearance more. I'm not going to do this right now and will just see how it works with the 27mm EDF.

Now it's just a matter of getting my temp sensor hooked up, running the wires through, and getting the cover back on. I'll also have to figure out what I'm going to use to fill the gap between the air duct and motor case, something that the side cover will easily wear away and make a tight fit.